This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To determine noninvasively the effects of aging and reduced caloric intake on the physiological measures of [unreadable] sensitivity to sound stimuli.[unreadable] [unreadable] Progressive sensorineural hearing loss (presbycusis) beginning in middle age is typical in humans. The change [unreadable] predominantly affects high- frequency tones. Reduced caloric intake (CR) has beneficial effects on aging in several [unreadable] models. This subproject assesses the effects of moderate CR on auditory evoked potentials in rhesus monkeys [unreadable] eating ad libitum compared to a reduced food allotment. [unreadable] [unreadable] Thresholds were measured using auditory brainstem responses (ABR). Click thresholds increased with age, but [unreadable] indicated no difference with respect to diet group. For click thresholds, there was no progression of hearing loss [unreadable] over the past five years in either group as measured with click stimuli. These data may reflect the fact that some [unreadable] of the older monkeys whose thresholds would be expected to increase further with age had died in the intervening [unreadable] five years between assessments. ABR thresholds were also determined for 8, 16, and 32 kHz tone pips. [unreadable] Thresholds increased for each of these frequencies with aging. Threshold increases with age were minimal for 32 [unreadable] kHz, however, probably reflecting a ceiling effect as many thresholds reached equipment limits for older monkeys. [unreadable] [unreadable] Distortion product otoacoustic emissions (DPOAE) are very low amplitude sounds emitted from the normal cochlea. In [unreadable] both humans and rhesus monkeys, decreased amplitudes of DPOAEs have been documented in relation to aging. In [unreadable] this study, the effects of CR on hearing, as measured with DPOAEs, were not found to result in significant preservation [unreadable] of auditory function. In fact, DPOAE amplitudes with aging were either statistically the same or significantly reduced in [unreadable] the CR group compared to the controls. [unreadable] [unreadable] In the current report period, we evaluated physiological function of the middle ear in these animals. Results parallel [unreadable] those in aging humans, i.e., we observed reduced peak compensated static acoustic admittance. Longitudinal studies are [unreadable] now underway.[unreadable] [unreadable] We plan to continue these assessments on the effects of age, sex, and diet as the animals age. This research used [unreadable] WNPRC Animal Services and Aging Resources.